1. Field of the Invention
The present invention concerns an improved device to form the selvedge in shuttleless looms.
It is known that, in any type of such looms, suitable transport means (such as shuttles grippers, projectiles, air or water means) insert an appropriate sequence of weft yarns into the sequence of warp yarns forming the shed.
In the case of shuttle looms, the warp yarns at the edges of the fabric, forming the so-called selvedge, are woven by the same weft which repeatedly moves into and out of the warp shed, after said warp yarns have exchanged their position, so as to obtain the wanted weave.
As is known, such fabrics are characterized by even edges, which stand particularly well any subsequent finishing and printing treatments.
In shuttleless looms (gripper, projectile, fluid jet, air and water looms) it is not possible to obtain the same selvedge which can be formed with shuttle looms. On the other hand, to form a sufficiently strong and even selvedge, special devices have to be used, which weave together the outer warp yarns and the inserted weft yarns.
2. Description of the Prior Art
Among the different devices already used for this purpose, there are known to be mechanical devices called "tuck-in selvedge devices".
These devices allow a succession of co-ordinated movements to be performed by mechanical members, in order to carry out the following operations:
1) A mechanically or pneumatically controlled gripping member (for instance a gripper) seizes the weft yarn which has just been inserted after the reed has started its opening movement.
2) A cutting member, such as a shear, cuts the weft yarn just seized by the gripper at a suitable distance from the edge of the fabric.
3) A needle performs a translatory and rotary motion, inserting its hook-shaped tip into a proper position of the warp shed, and then moves back towards the gripper separating a suitably wide strip of warp yarns.
4) The gripper winds the weft yarn around the hook-shaped needle tip.
5) The needle, with a rotary movement, inserts the weft tail, cut to size, into the strip of warp yarns.
Fabric selvedges thus formed look like those which can be obtained with shuttle looms; the edges are hence even and strong.
The tuck-in selvedge devices used on currently known shuttleless looms provide for the aforecited members to be moved mechanically, by lever and/or cam kinematic mechanisms, or else pneumatically.
Particularly in shuttleless looms for terry cloth weaving--both in the case of shifting the reed beat-up point and in the case of shifting the fabric--the wefts to be tucked in during the loop forming cycle, which can last three or four weft insertions, are at different distances in respect of the selvedge forming device.
In order to obtain the tuck-in of the weft, it would hence be necessary to be able to suitably vary cyclically the longitudinal stroke of the needle or else, keeping the needle stroke fixed, to perform the tuck-in at different times of the loom working cycle, in correspondence of which times the weft is at the weft is at the same distance from the tuck-in device.
It should also be noted that in terry cloth weaving looms, besides the aforementioned weaving to form the loop, other weavings are performed which could require weft tuck-in after each weft insertion, and in which the weft is at the same distance from the device. In such cases, no change in the longitudinal stroke of the needle is hence required.
The currently known selvedge forming devices do not allow to obtain the above desired performances, in that it is not possible to continuously vary, in devices making use of mechanical elements like cams and levers, the strokes and phases of the needle and gripper motion during operation.
A known solution, allowing to partly overcome the problem, is to tuck in the weft--also with the possibility of selection--after a number of wefts has been inserted, to which there corresponds--for the type of weaving being performed--an equal position of the weft in resect of the device and thus in respect of the needle. Usually, in terry cloth weaving looms, this takes place at the end of the beat-up forming the loop. Such devices therefore realize the simultaneous tuck-in of three or four weft tails in the terry cloth weave, which can cause shear cutting problems or require a needle with a large hook.